Conjugated Energetic Salts Based on Fused Rings: Insensitive and Highly Dense Materials

Abstract

Nitroamino-functionalized 1,2,4-triazolo­[4,3-b]­[1,2,4,5]­tetrazine (1), when combined with intermolecular hydrogen bonds (HBs) and strong noncovalent interactions between layers, results, for example, in an interlayer distance of 2.9 Å for dihydroxylammonium 3,6-dinitramino-1,2,4-triazolo­[4,3-b]­[1,2,4,5]­tetrazine (2c) with a packing coefficient of 0.805. For dihydroxylammonium 6,6′-dinitramino-3,3′-azo-1,2,4-triazolo­[4,3-b]­[1,2,4,5]­tetrazine (3b), two fused rings are linked by an azo group, which expands the conjugated system resulting in an even shorter interlayer distance of 2.7 Å and a higher packing coefficient of 0.807. These values appear to be the shortest interlayer distances and the highest packing coefficients reported for tetrazine energetic materials. With high packing coefficients, both possess high densities of 1.92 g cm–3 and 1.99 g cm–3 at 293 K, respectively. Compared with its precursor, the hydroxylammonium moiety serves as a buffer chain (H–N–O–H), connecting the anion and cation through hydrogen bonds, giving rise to more favorable stacking, and resulting in higher density and lower sensitivity. The sensitivities of all the hydroxylammonium salts are lower than that of their neutral precursors, such as compound 2 (3 J, >5 N) and compound 2c (25 J, 360 N). The detonation properties of 2c (detonation velocity vD = 9712 m s–1 and detonation pressure P = 43 GPa) and 3b (vD = 10233 m s–1; P = 49 GPa) exceed those of present high explosive benchmarks, such as octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and hexanitrohexaazaisowurzitane (CL-20). The molecular structures of several of these new energetic materials are confirmed by single-crystal X-ray diffraction measurements. Using calculated and experimental results, the fused ring with a planar large π-conjugated system results in a compromise between desirable stabilities and high detonation properties, thus enhancing future utilization in the design of energetic materials.

Coplanar Fused Heterocycle‐Based Energetic Materials

“…Nitroamino‐functionalized 1,2,4‐triazolo[4,3‐b][1,2,4,5]‐tetrazine fused rings including 6‐nitramino‐1,2,4‐triazolo[4,3‐b][1,2,4,5]tetrazine ( 2 ), 3,6‐dinitramino‐1,2,4‐triazolo[4,3‐b]‐[1,2,4,5] tetrazine ( 3 ), and their nitrogen‐rich salts were reported by Shreeve et al. in the first time (Scheme ) . Figure shows that the structures of two large conjugated anions were all nearly planar.…”

“…Triazolo tetrazine or triazolo triazine are promising structures in designing new energetic materials owing to the advantages of the conjugated system and they have several positions for modification where energy-rich functional groups may well be introduced [38]. [39]. Figure 2 shows that the structures of two large conjugated anions were all nearly planar.…”

The Ingenious Synthesis of a Nitro-Free Insensitive High-Energy Material Featuring Face-to-Face and Edge-to-Face π-Interactions

“…Recently it has been observed by Shreeve group that energetic materials with parallel face-to-face crystal stacking are found to show higher densities and relative low sensitivities because of π-stacked interaction and free interlayer sliding (Yin et al, 2016; Liu et al, 2019). This type is strikingly represented by fused energetic compounds (Figure 1B) (Thottempudi et al, 2014; Tang et al, 2017; Hu et al, 2018; Wang et al, 2019).…”

Sensitive Energetics from the N‐Amination of 4‐Nitro‐1,2,3‐Triazole

“…Within the field of energetic materials, the development of new explosives possessing high performance and high stability is a major goal. [1][2][3][4][5][6][7] Unfortunately, many examples exist suggesting that high performance and high stability are often mutually exclusive. There are three main ways to impart explosive energy content to an energetic molecule; the incorporation of fuel and oxidizer in the same molecule (as seen in traditional energetics such as RDX and PETN), creating compounds possessing ring or cage strain, and incorporating large amounts of nitrogen to give rise to high heats of formation.…”